Method and apparatus for producing steel intermediate products

ABSTRACT

Methods and apparatuses for continuously producing steel intermediate products are disclosed. Liquid steel is cast into plural moulds to continuously produce plural bloom strands using continuous casting apparatus. Subsequently, one or more of the bloom strands is fed in-line to respective rolling mills configured to hot roll the input continuously cast bloom strands to produce rolled billets.

RELATED APPLICATIONS

This application claims priority to, and the benefit of, GB patentapplication no. GB1417999.8, filed Oct. 10, 2014, and GB patentapplication no. GB1517278.6, filed Sep. 30, 2015. The text of each ofthese applications is incorporated herein in its entirety.

FIELD OF THE TECHNOLOGY

The present invention relates generally to methods and apparatuses forproducing steel intermediate products. In particular, the presentdisclosure relates to methods and apparatuses for in-line rolling ofbillets from continuously cast blooms.

BACKGROUND

Rolling mills are installed for producing finished steel products, forexample, for local markets in developing world countries and nearmarkets for finished steel products, such as mild steel bar for use incivil construction. In countries where there is no significantproduction of semi-finished (cast) steel products, these rolling millswill typically rely on importing steel billets from other countries thathave a larger steelmaking capacity, to finish for their local markets.This is prevalent in many developing world countries because even localproduction of steel intermediate products from recycled steel is notpossible due to the scarcity of steel scrap generated locally, and thedifficulties with providing a reliable and cost-effective supply ofelectrical power to operate an electric arc furnace. Therefore, importedbillets are ‘re-rolled’ to produce the finished steel products. These‘re-rolling mills’ typically take a starting billet size of up to 150 mmby 150 mm square (225 square centimetres) and are typically much smallerand have fewer production capabilities in terms of variety of input andoutput products, and production rate, compared to larger, dedicatedrolling mills.

In the 1960s, production of billets was achieve by rolling cast ingots,each weighing 10 tons or more and such ingots were rolled into billetsin a separate billet rolling mill. This antiquated method had no problemwith rolling the ingots into the 150 mm needed for the re-rolling millsdescribed above. However, such a billet production method resulted inhigh end losses and has additional rolling costs, and so it was notparticularly effective or efficient.

Since the 1970s, the “Continuous Casting” process has completelyreplaced the old ingots casting practice for producing intermediatesteel products, and so now square or round billets are typicallydirectly casted from liquid steel using a “Continuous Casting Machine”,rather than being rolled from cast ingots.

With today's very large capacity steel mills, producing, say, over 2million tons of steel products annually, the continuously casted billetsare of much larger cross section than is capable of being rolled by a‘re-rolling’ mill. For example, continuous casting machines producing“bloom” strands having a cross section of greater than 150 mm by 150 mmsquare, and up to 400 mm by 400 mm square (typically 240 mm by 240 mmsquare or in the case of a tube continuous casting machine, 250 mmround) are now commonplace at the larger steel producing facilities.These blooms are larger than the typical maximum size billet of 150 mmby 150 mm square that can be rolled by the re-rolling mills describedabove.

It is in this context that the present disclosure is devised.

SUMMARY

Viewed from one aspect, the present disclosure provides a method ofcontinuously producing steel intermediate products. The method includescasting liquid steel into plural moulds to continuously produce pluralbloom strands; and feeding one or more of the bloom strands in-line torespective rolling mills configured to be selectively engageable to hotroll the input continuously cast bloom strands to produce rolledbillets, wherein the rolling mills comprise two or more cantileverrolling mill stands in which bearing supports for the rollers of eachstand support the rollers at only one end, and wherein the angle of theaxes of the rollers of the first cantilever rolling mill stand for agiven bloom is set at 45 degrees to the top surface of the bloom andwherein the angle of the axes of the subsequent rolling mill stands isset at 90 degrees to each other.

In accordance with the present disclosure, excess steel bloom productionby a large capacity continuous steel casting machine can be directlyconverted to billets by an in-line hot rolling process, without the needfor additional heating or reheating of the blooms before rolling. Inthis way, there is no need for a separate billet rolling mill to producere-rollable billets from the continuously cast blooms, and as a result,this additional investment, double handling, extra manning, heating androlling losses that would result from rolling reheated bloom lengths andwhich would make such billet production uneconomical, is avoided. Inthis way, large capacity multi-strand continuous casting machines areenabled to efficiently directly produce re-rollable billets by anin-line rolling process at the same time as producing larger blooms. Byenabling, preferably selectable, production of readily-exportablebillets directly from continuously cast bloom strands, large capacitysteel intermediate production facilities can export surplus productionfor use in re-rolling mills in countries that rely on importing steelbillets.

In embodiments, the cast bloom strands fed in-line to the rolling millsare still hot from the continuous casting, and wherein no additionalreheating of the blooms is performed between the casting and hotrolling.

Preferably, the bloom strands have a cross sectional area above 230square centimetres, and preferably the rolled billets have a crosssectional area below 230 square centimetres. Blooms typically aredimensioned above 150 mm square (and up to 400 mm square), the rolledbillets typically are dimensioned below 150 mm square.

In embodiments the method further comprises: feeding the bloom strandsthrough respective straightening rollers; operating each rolling mill ata speed based on a reference speed of the straightening rollers of theparticular bloom strand fed to that rolling mill. Using the speed of theindividual straightening rollers for each continuously cast strand as areference speed for the rolling speed of the rolling mill for thatstrand in this way enables the billets to be reliably hot rolled and thematerial flow balance to be maintained on a strand-by-strand basis.

The use of cantilevered rolling mill stands allows the rolling of eachbloom strand to not interfere with the adjacent strand of themulti-strand bloom casting machine, and it allows the length of therolling mill across all stands to be kept low and to be positioned asclose as possible to the exit of the strands from the continuous castingmachine, enabling the blooms to be rolled while still hot from thecasting process, and before they have cooled. Conventional rollingmills, in which the rollers are “simply supported” with bearing supportsat both ends of the rolling axis, would be too large to fit between theadjacent strands on exit from the continuous casting machine, and sowould only be usable to roll the cast blooms if the strands were spacedfurther apart on exit from the continuous casting machine or movedfurther apart somehow by rollers. This is simply not practical.

In embodiments the drive mechanism and motor for each cantilever rollingmill stand is arranged outside the outermost strands produced by thecontinuous casting. In this way the bulky drive mechanism and motorcomponents will not occupy space immediately above or below the bloomstrands, such that the cast blooms are not interfered with.

In embodiments the drive mechanism and/or motor for the or eachcantilever rolling mill stand is connected to the respective cantileverrolling mill stand by respective long shafts arranged so as to distancethe drive mechanism and/or motor from the hot blooms. This enables thedrive equipment and motors to be operated away from the high temperatureenvironment immediately surrounding the cast blooms, improving theirlifetime and reliability, and allowing conventional motors andmechanisms to be used that are not required to be designed to withstandextreme environments and temperatures.

In embodiments each of the rolls for a given cantilever rolling millstand is driven by an individual motor.

In embodiments the angle of the axes of the subsequent rolling millstands is set at 90 degrees to each other. Arranging the cantileveredrolling mill stands in this way allows the rollers to access the bloomstrands from away to the sides of the bloom, reducing the extent towhich the rollers and the rolling mill housing interfere with the spaceimmediately surrounding the cast blooms. Further, by alternating theaxes of the rollers in this way, the rolling mill housings and standscan be offset from each other and/or positioned alternately above andbelow the cast blooms allowing the rollers to be positioned close toeach other axially along the strand, allowing the rolling mill to occupya short length along the strand such that the cast strand can be rolledat a uniform temperature without significant cooling between the rollingmill stands. In embodiments each rolling mill comprises at least two, orpreferably at least four, in-line cantilever rolling mill standsarranged to roll increasingly small billet sizes. In embodiments, eachrolling mill stand will work on two faces of the bloom (for example, ifthe bloom is a 240 mm by 240 mm square cross section bloom) and the nextrolling mill stand will work on the opposite two faces, rolling the castblooms into smaller size billets.

In embodiments, it may not be desirable to further roll the bloomstrands. Therefore the cantilever stands may be moved out of the line ofthe bloom casting without interrupting the casting process. The rolls ofcantilever stands are separated from each another to at least a distancewide enough for the rolling mill stands to clear the bloom and be movedout of the bloom casting line.

In embodiments the housing for the bearing supports for each cantileverrolling mill stand is configured as a replaceable cassette, for example,that interfaces with the motor and drive mechanism. This will facilitatea quick changing of the rolls, for example when the rolls become worn,reducing downtime.

In embodiments, the rolling mill and each rolling mill stand isselectably operable or engageable with the cast blooms, allowing thebloom strands to be selectably hot rolled into billets optionally ofvarying sizes. This allows the output of the continuous casting machineto be selectably variable in size, allowing production to adapt readilyto demand, for example, fluctuations in demand in domestic and/or exportmarkets for cast blooms and (rolled) billets.

In embodiments protective cooling or insulating jackets are providedaround the housing for the bearing supports and/or the motor and/ordrive mechanism for each cantilever rolling mill stand.

In embodiments only one or both of the outermost strands of theplurality of continuously cast bloom strands is hot rolled into abillet. By rolling only the outermost strand(s), the degree to which therolling mill interferes with the space around the cast bloom strands,and the degree to which the steel mill needs to be re-engineered toaccommodate the rolling mill is minimized. In addition the requirementsfor the rolling mill stands are less stringent as the space requirementsfor rolling only the outermost strand(s) (due to the space availabilityto the sides of the strands) are less than those required for theinnermost strands. In addition, excess production of continuously castblooms, for example, for the domestic market, can, by operating on theoutermost bloom strands, easily be hot rolled in-line into billets inthe continuous casting process for direct export, for example, todeveloping world countries for re-rolling in a billet re-rolling mill.

Viewed from another aspect, the present disclosure provides apparatusfor continuously producing steel intermediate products. The apparatuscomprises a continuous casting apparatus arranged to, in use,continuously produce plural bloom strands; and one or more in-linerolling mills each arranged to be selectively engageable to receive andhot roll, in use, one of the continuously cast bloom strands to producerolled billets, wherein the rolling mills comprise two or morecantilever rolling mill stands in which bearing supports for the rollersof each stand support the rollers at only one end, and wherein the angleof the axes of the rollers of the first cantilever rolling mill standfor a given bloom is set at 45 degrees to the top surface of the bloomand wherein the angle of the axes of the subsequent rolling mill standsis set at 90 degrees to each other.

In embodiments the continuous casting apparatus comprises a tundisharranged to collect liquid steel and provide said liquid steel to pluralmoulds arranged side by side to continuously produce plural bloomstrands.

In embodiments, the continuous casting apparatus is configured tooperate in the methods in accordance with the embodiments describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure, may best be understood by reference to the followingdescription of certain exemplary embodiments together with theaccompanying drawing in which:

FIG. 1 illustrates an apparatus and method of operation thereof forin-line rolling of billets from continuously cast blooms in accordancewith an embodiment of aspects of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The detailed description set forth below in connection with the appendeddrawings is intended as a description of presently preferred embodimentsof the disclosure, and is not intended to represent the only forms inwhich the present disclosure may be practised. It is to be understoodthat the same or equivalent functions may be accomplished by differentembodiments that are intended to be encompassed within the spirit andscope of the disclosure. Furthermore, terms “comprises,” “comprising,”or any other variation thereof, are intended to cover a non-exclusiveinclusion, such that apparatuses and method steps that comprises a listof elements or steps does not include only those elements but mayinclude other elements or steps not expressly listed or inherent. Anelement or step proceeded by “comprises . . . a” does not, without moreconstraints, preclude the existence of additional identical elements orsteps that comprises the element or step.

Referring now to FIG. 1, which shows an apparatus 100 for in-linerolling of billets from continuously cast blooms in accordance with anembodiment of the present disclosure, a continuous casting machine 110comprises a ladle 112, tundish 114, multiple permanent moulds 116 forforming strands 118 and straightening rollers 120 for straightening thestrands.

Molten steel is tapped into the ladle 112 from one or more furnaces (notshown). The ladle 112 has at its bottom a pipe opening which is arrangedabove and drains liquid steel into a holding bath or tundish 114. Thetundish 114 acts as a buffer reservoir and has shrouds or pipe openingsinto the permanent moulds 116. The liquid steel drains from the tundish114 into the permanent moulds 116 which are shaped and liquid cooled toform a solidified exterior casing for the strands 118 that are formed bythe hardened steel dropping due to gravity from the open bottom of thepermanent moulds 116. In this case, five permanent moulds 116 areprovided, but the number of permanent moulds could be greater or fewerthan this, but is preferably at least two, and even more preferablygreater than two or an even higher number in order to give a highproduction capacity. Each of the continuously cast strands 118 is thenpassed through sequences of pairs of individual straightening rollersthat guide the strands to extend in a horizontal direction andstraighten the strands as they move along between the rollers and cooland further solidify.

The continuous casting machine 110, and the permanent moulds 116 inparticular are configured such that the strands 118 are formed as bloomshaving a cross sectional area above 230 square centimetres, in this case240 mm by 240 mm square.

The continuous casting machine 110 has a high production capacity of,say 2 million tonnes a year, with a production speed of at least 4metres per minute, and can operate continuously for a number of years ofproduction between servicing. When this production capacity ofcontinuously cast blooms exceeds demand, for example in the domesticmarket, which would lead to an increase in inventory of cast blooms, inaccordance with the present disclosure, the apparatus 100 operates tohot roll one or more of the bloom strands 118 into billets 140 byoperation of the in-line rolling mills 150, which can for example beexported to developing world markets for direct use in re-rolling mills.The rolled billets are formed to have a cross sectional area below 230square centimetres, in this case 150 mm by 150 mm square.

The apparatus 100 is arranged such that the cast bloom strands 118 fedin-line to the rolling mills 140 in use are still hot from thecontinuous casting. No apparatus is provided arranged to performadditional reheating of the blooms between the casting and hot rolling.

The in-line rolling mills 150 comprise a plurality of cantilever rollingmill stands 152 in which the bearing supports for the rollers 154 ofeach stand support the rollers at only one end. The drive mechanism andmotor 156 for each cantilever rolling mill stand 152 is arranged outsidethe outermost strands 118 produced by the continuous casting. Inembodiments different to that shown in FIG. 1, the drive mechanismand/or motor 156 for the cantilever rolling mill stands 152 can beconnected to the respective cantilever rolling mill stand 152 byrespective long shafts arranged so as to distance the drive mechanismand/or motor 156 from the hot blooms 118. To further reduce heatingeffects, in other embodiments protective cooling or insulating jacketscan be provided around the housing 158 for the bearing supports and/orthe motor and/or drive mechanism 156 for each cantilever rolling millstand 152. Motors may be arranged to individually drive each of therollers 154 for a given cantilever rolling mill stand 152.

For clarity's sake, in FIG. 1, the second cantilevered rolling millstand 152 of each rolling mill is drawn with the drive mechanism andmotor 156 and the housing 158 below the strands 118 at floor level.However, in other embodiments, to avoid mill scale build up on themachinery, the rolling mills 150 can be arranged such that the drivemechanism and motor 156 and the housing 158 of the cantilevered rollingmill stands 152 are never positioned underneath the strands 118 by, forexample, positioning certain components above floor level.

The housing 158 for the bearing supports for each cantilever rollingmill stand 152 is configured as a replaceable cassette, for facilitatinga quick changing of the rolls, e.g. when worn, reducing down time.

Each rolling mill 150 (for each strand) comprises two in-line cantileverrolling mill stands 152. In other embodiments, more than two orpreferably at least four, cantilever rolling mill stands are provided,arranged to roll increasingly small billet sizes. The angle of the axesof the rollers of the first cantilever rolling mill stand for a givenbloom is set at 45 degrees to the top surface of the bloom. The angle ofthe axes of the subsequent rolling mill stands is set at 90 degrees, orabout 90 degrees, to each other.

Each rolling mill 150 is configured to operate at a speed based on areference speed of the straightening rollers of the particular bloomstrand 118 fed to that rolling mill. This ensures a balance to the flowof material through the rolling mills 150.

As shown in FIG. 1, both of the outermost strands of the plurality ofcontinuously cast bloom strands 118 is hot rolled into a billet. Thein-line rolling mills 150 are in position and operate continuously suchthat rolled billets are always produced. The rolling mills 150 can beselectively engaged such that billet production can be responsive tovariation in demand for cast bloomed and rolled billets for re-rolling.Therefore the cantilever stands may be moved out of the line of thebloom casting without interrupting the casting process. The rollers 154of the cantilever stands are separated from each another to at least adistance wide enough for the rolling mill stands 150 to clear the bloomand be moved out of the bloom casting line.

The disclosure is applicable not just to square blooms, but also toround blooms for which appropriate permanent moulds and straighteningrollers need to be provided. The roll pass section then needs to beadjusted accordingly to produce billets of the desired square (or other)cross section.

In a further embodiment of the present disclosure, the strands are castin a process of sequence continuous casting. This process enablesdifferent temperatures of liquid steel to be continuous-continuouslycasted, i.e. without interruption. This process increases productivityby eliminating the need to prepare for starting a new individual castingprocess each time. Through the use of adjustable cantilevered rollingmill stands the present disclosure allows for the blooms width to beadjusted and liquid steel of different temperatures to be castcontinuously. Steel of different temperatures may be utilised byreplacing the tundish comprising the steel of a different temperature.

The description of the preferred embodiments of the present disclosurehas been presented for purposes of illustration and description, but isnot intended to be exhaustive or to limit the disclosure to the formsdisclosed. It will be appreciated by those skilled in the art thatchanges could be made to the embodiments described above withoutdeparting from the broad inventive concept thereof. It is understood,therefore, that this disclosure is not limited to the particularembodiment disclosed, but covers modifications within the scope of thepresent disclosure as defined by the appended claims.

1. A method of continuously producing steel intermediate products,comprising: casting liquid steel into plural moulds to continuouslyproduce plural bloom strands; and feeding one or more of the bloomstrands in-line to respective rolling mills configured to be selectivelyengageable to hot roll the input continuously cast bloom strands toproduce rolled billets, wherein the rolling mills comprise two or morecantilever rolling mill stands in which bearing supports for the rollersof each stand support the rollers at only one end, and wherein the angleof the axes of the rollers of the first cantilever rolling mill standfor a given bloom is set at 45 degrees to the top surface of the bloomand wherein the angle of the axes of the subsequent rolling mill standsis set at 90 degrees to each other.
 2. A method as claimed in claim 1,wherein the cast bloom strands fed in-line to the rolling mills arestill hot from the continuous casting, and wherein no additionalreheating of the blooms is performed between the casting and hotrolling.
 3. A method as claimed in claim 1, wherein the bloom strandshave a cross sectional area above 230 square centimetres, and whereinthe rolled billets have a cross sectional area below 230 squarecentimetres.
 4. A method as claimed in claim 1, further comprising:feeding the bloom strands through respective straightening rollers; andoperating each rolling mill at a speed based on a reference speed of thestraightening rollers of the particular bloom strand fed to that rollingmill.
 5. A method as claimed in claim 1, wherein a drive mechanism and amotor for each cantilever rolling mill stand is arranged outside theoutermost strands produced by the continuous casting.
 6. A method asclaimed in claim 1, wherein each of the rolls for a given cantileverrolling mill stand is driven by an individual motor.
 7. A method asclaimed in claim 1, wherein each rolling mill comprises at least two, orpreferably at least four, in-line cantilever rolling mill standsarranged to roll increasingly small billet sizes.
 8. A method as claimedin claim 1, wherein a housing for the bearing supports for eachcantilever rolling mill stand is configured as a replaceable cassette.9. A method as claimed in claim 1, wherein protective cooling orinsulating jackets are provided around a housing for the bearingsupports and/or a motor and/or a drive mechanism for each cantileverrolling mill stand.
 10. A method as claimed in claim 1, wherein only oneor both of the outermost strands of the plurality of continuously castbloom strands is hot rolled into a billet, and wherein at least oneinnermost bloom strand is provided.
 11. A method as claimed in claim 1,wherein the plural bloom strands are cast in a process of sequencecontinuous casting.
 12. A method as claimed in claim 1, wherein therollers of the cantilever rolling mill stands are separated from eachanother to at least a distance wide enough for the cantilever rollingmill stands to clear the bloom and be moved out of the bloom castingline.
 13. Apparatus for continuously producing steel intermediateproducts, comprising: continuous casting apparatus arranged to, in use,continuously produce plural bloom strands; and one or more in-linerolling mills each arranged to be selectively engageable to receive andhot roll, in use, one of the continuously cast bloom strands to producerolled billets, wherein the rolling mills comprise two or morecantilever rolling mill stands in which bearing supports for the rollersof each stand support the rollers at only one end, and wherein the angleof the axes of the rollers of the first cantilever rolling mill standfor a given bloom is set at 45 degrees to the top surface of the bloomand wherein the angle of the axes of the subsequent rolling mill standsis set at 90 degrees to each other.
 14. Apparatus as claimed in claim13, wherein the apparatus is arranged such that the cast bloom strandsfed in-line to the rolling mills in use are still hot from thecontinuous casting, and wherein no apparatus is provided arranged toperforming additional reheating of the blooms between the casting andhot rolling in use.
 15. Apparatus as claimed in claim 13, whereincontinuous casting apparatus comprises a tundish arranged to collectliquid steel and provide said liquid steel to plural moulds arrangedside by side to continuously produce plural bloom strands.
 16. Apparatusas claimed in claim 13, wherein the continuous casting apparatus isconfigured to produce bloom strands having a cross sectional area above230 square centimetres, and wherein the in-line rolling mills areconfigured to roll billets having a cross sectional area below 230square centimetres.
 17. Apparatus as claimed in claim 13, furthercomprising: for each bloom strand, respective straightening rollersarranged to receive and straighten the bloom strand; wherein eachrolling mill is configured to operate at a speed based on a referencespeed of the straightening rollers of the particular bloom strand fed tothat rolling mill.
 18. Apparatus as claimed in claim 13, wherein a drivemechanism and a motor for each cantilever rolling mill stand is arrangedoutside the outermost strands produced by the continuous casting. 19.Apparatus as claimed in claim 13, further comprising motors arranged toindividually drive each of the rolls for a given cantilever rolling millstand.
 20. Apparatus as claimed in claim 13, wherein the angle of theaxes of the subsequent rolling mill stands is set at 90 degrees to eachother.
 21. Apparatus as claimed in claim 13, wherein each rolling millcomprises at least two, or preferably at least four, in-line cantileverrolling mill stands arranged to roll increasingly small billet sizes.22. Apparatus as claimed in claim 13, wherein a housing for the bearingsupports for each cantilever rolling mill stand is configured as areplaceable cassette.
 23. Apparatus as claimed in claim 13, furthercomprising protective cooling or insulating jackets provided around ahousing for the bearing supports and/or a motor and/or a drive mechanismfor each cantilever rolling mill stand.
 24. Apparatus as claimed inclaim 13, wherein only one or both of the outermost strands of theplurality of continuously cast bloom strands is hot rolled into abillet, and wherein at least one innermost bloom strand is provided. 25.Apparatus as claimed in claim 13, wherein the plural bloom strands arecast in a process of sequence continuous casting.
 26. Apparatus asclaimed in claim 13, wherein the rollers of the cantilever rolling millstands are separated from each another to at least a distance wideenough for the cantilever rolling mill stands to clear the bloom and bemoved out of the bloom casting line.